The present invention relates to a process for producing multiple color articles by injection molding, and more particularly to a process which combines separate, discrete bands or patterns of different colors in intertwined fashion.
Prior to the present invention, the vast majority of toothbrush handles and similar items has been made up of rather plain, one-color items occasionally decorated with paint, embossing or decals. As both dental science and modern tastes have developed, it has become increasingly clear that frequent brushing is beneficial to dental health, and that the addition of bright colors, stripes and other visually attractive elements to ordinary items such as jogging shoes, sweat shirts, dental floss, and sweat pants increases public interest in the otherwise dull but beneficial activities they support.
Attempts to create visually more attractive or interesting articles such as toothbrushes were limited in that the less expensive methods of decoration--embossing, paint, and decals--added very little visual appeal, were subject to deterioration with wear, or posed potential health problems in situations in which the article was placed in the user's mouth, as with toothbrush handles. More expensive techniques for manufacturing multicolored plastic articles suitable for use as handles were not feasible since the articles themselves have strictly limited useful lives and therefore their price must be kept low.
Injection molding techniques for producing articles with separate areas of different-color materials have been known. For example, see Danielson et al. U.S. Pat. No. 2,663,910, directed to a method for molding a multipart plastic structure. The Danielson patents shows a two-step molding procedure, but one suitable only for producing relatively simple articles such as poker chips, telephone buttons and other plastic items with indicia on the item's face. Although the method of the Danielson patent included the precasting of a preliminary molded part, that method did not include the principles of the present invention described below.